1. Field of the Invention
This invention relates to an electrophotographic apparatus for forming visible images corresponding to picture information on a recording medium by developer which is adapted for use as picture output devices, such as facsimile, copying machine, laser printer, LED printer, and liquid crystal printer, and, more particularly, to an improvement of an electrophotographic apparatus of the so-called shell-open type wherein an upper unit is open-/close-able with respect to a lower unit.
2. Description of the Prior Art
Recently, in order to miniaturize the electrophotographic apparatus and facilitate its maintenance, as shown in FIGS. 3 and 4, the so-called shell-open type of electrophotographic apparatus 1 has been devised wherein an upper unit 2 is open-/close-able with respect to a lower unit 3. This electrophotographic apparatus 1 will first be described with reference to FIGS. 3 and 4.
The upper unit 2 is supported pivotably by a horizontal support shaft 5 held by a bracket 5 provided in the end portion of the lower unit 3, and a cartridge unit 6 is equipped laterally detachably to the upper unit 2 which supports a sensitizing drum 7 whose lower part is opened to the exterior. In the cartridge unit 6 there are attached so as to surround the sensitizing drum 7 an electrifying unit 8 for electrifying the electrophotographic apparatus 1 to a certain potential through corona discharge, a developing unit 9 for attracting toner and attaching to electrostatic latent images on the sensitizing drum 7 by the use of a developing roll 10 to thereby form visible images, and a cleaner 11 for mechanically removing the toner remaining on the sensitizing drum 7. Inside the upper unit 2 there is mounted an optical writing unit 12 for forming electrostatic latent images corresponding to the picture information of a copy on the sensitizing drum 7 having been given a uniform charge by the electrifying unit 8.
On the other hand, a paper feed cassette 14 is provided detachably in the end portion of the lower unit 3, which stores therein a number of recording papers 13 piled one upon another. Inside the lower unit 3 and above the end portion of the paper feed cassette 14 there is disposed a paper feed roller 15 for supplying the recording papers 13 stored in the paper feed cassette 14 one after another.
Further, inside the lower unit 3 there is formed a conveyor path 16 for horizontally conveying the recording paper 13 given from the paper feed cassette 14, which includes a plurality of pairs of conveyor rollers 17, 17 arranged therein. Furthermore, in the end portion of the conveyor path 16 there is provided a fixing unit 18 for fixing the toner attached to the recording paper 13. The recording paper 13 passed through the fixing unit 18 is ejected onto a tray 20 by ejecting rollers 19, 19. In addition, a transfer unit 21 is provided below the conveyor path 16 at a position coming into opposition to the lower part of the sensitizing drum 7 disposed in the upper unit 2 when the upper unit 2 is closed.
When to form a picture on the recording paper 13 by the use of the foregoing configuration, with keeping the upper unit 2 in the closed state, the sensitizing drum 7 is electrified to a certain potential by the electrifying unit 8 and an electrostatic latent image is formed through exposure on the surface of the sensitizing drum 7 by means of the optical writing unit 12. Thereafter, the toner in the developing unit 9 is attracted by the developing roll 10 and attached selectively to the sensitizing drum 7, whereby a visible image corresponding to the electrostatic latent image is formed. During the above process one recording paper 13 is supplied from the paper feed cassette 14 to the conveyor path 16 by the paper feed roller 15, and when this recording paper 13 comes to the station between the sensitizing drum 7 and the transfer unit 21, the visible image on the sensitizing drum 7 is transferred to the recording paper 13 by causing corona discharge from the back of the recording paper 13 by means of the transfer unit 21. The thus transferred visible image is fixed on the recording paper 13 by the fixing unit 18 and then the paper is ejected onto the tray 20.
On the other hand, residual surface potential existing in non-exposed portions of the sensitizing drum 7 is optically made to zero potential by a de-electrifying light source not shown, and the toner not transferred and remaining on the sensitizing drum 7 is removed from the electrophotographic apparatus 1 by the cleaner 11.
In the conventional electrophotographic apparatus 1 described above, if jamming occurs when the recording paper 13 comes out of the paper feed cassette 14 or while it is being conveyed through the conveyor path 16, usually, the recording paper 13 under trouble is pulled out by pivoting the upper unit 2 about the support shaft 5 and opening the upper part of the lower unit 3, as shown in FIG. 4. But, this opened state causes inevitably the lower part of the sensitizing drum 7 to be exposed. Thus, deterioration of the sensitizing drum 7 is accelerated as it is exposed to the light, and formation of the electrostatic latent image becomes questionable if the hand touches the sensitizing drum 7 erroneously when the recording paper 13 is taken out.
For overcoming the above drawbacks, another type of electrophotographic apparatus is also known in the prior art, as shown in FIG. 5, in which the cartridge unit 6 is provided with an arcuate drum cover 22 laterally movable in response to control of a lever not shown. This drum cover 22 is normally urged so as to cover the lower part of the sensitizing drum 7 by a spring, as illustrated by the imaginary line in FIG. 5, and as the upper unit is closed, can assume a retracted position as illustrated by the solid line in FIG. 5 by means of an arm not shown.
According to the configuration above, however, the sensitizing drum 7 of the cartridge unit 6 needs a space on its side for accommodating the drum cover 22, this making difficult miniaturization. Further, it has the problem that the range in which the light of a de-electrifying light source 23 for eliminating the residual potential of the sensitizing drum 7 reaches the sensitizing drum 7 becomes narrow; thus, the efficiency of de-electrification is degraded.